Stop brew tests dirtying the working tree

[dduugg]

brew tests points HOME at Library/Homebrew/test so local configuration cannot affect a run, which means any tool a spec shells out to writes into the checkout. mise left .local/state/mise/tracked-configs and .local/share/mise/migrations behind, untracked and never cleaned up. The tool is incidental, since anything that respects $HOME can do this, and it cannot be fixed from the other side: bin/brew filters the environment down to an allowlist, so exported XDG_* and MISE_* never reach the spec subprocesses.

The fix has two halves, each matching how brew already handles this. XDG_CACHE_HOME is redirected out of the test home on the line above, in 38ff362, so XDG_STATE_HOME is redirected the same way; nothing in brew reads it. XDG_DATA_HOME is deliberately not redirected, because unlike a cache or state directory it holds live tool installs, and pointing it elsewhere left a mise shim unable to resolve its own Ruby at all. What lands under it is gitignored instead, joining the six entries already there for tools that write into the test home: test/.gem, .cargo/, .homebrew/, .subversion, .npm/ and .rdbg_history. The entry is test/.local/share/ rather than test/.local/ on purpose, so that .local/state/ stays visible and a regression in the redirect still surfaces in git status instead of being silently ignored.

Repro, with mise installed:

HOME="$PWD/Library/Homebrew/test" mise current
ls Library/Homebrew/test/.local

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• Have you checked for other open Pull Requests for the same change?
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• I did not use AI/LLM to create this PR, or I disclosed the tool/model below and reviewed its output; I did not attribute commits to AI and will answer maintainer questions and review comments myself without AI/LLM.

AI/LLM disclosure: Claude Opus 5 via Claude Code helped trace the leak and draft the change; I reviewed it and confirmed the checkout stays clean across full test runs.

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[Copilot]

🟡 Changes recommended

Per-example cleanup introduces a cross-worker race, and the new environment redirect lacks regression coverage.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Redirects tool state away from the sandboxed test home and adds fallback cleanup.

Changes:

• Sets XDG_STATE_HOME to Homebrew’s test cache.
• Removes residual test/.local data during teardown.

File summaries

File	Description
Library/Homebrew/dev-cmd/tests.rb	Redirects test tool state.
Library/Homebrew/test/spec_helper.rb	Adds fallback state cleanup.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 2
• Review effort level: Balanced

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[Copilot]

🟡 Changes recommended

The fallback cleanup lacks regression coverage, and its comments reference a nonexistent API.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Review details

Suppressed comments (2)

Library/Homebrew/dev-cmd/tests.rb:283

• This repeats a reference to the nonexistent Cask::Utils.trash!; use the actual XDG-aware method name so the comment remains traceable to its implementation.

        # `XDG_DATA_HOME` is deliberately left alone: `Cask::Utils.trash!` reads it.

Library/Homebrew/dev-cmd/tests.rb:227

• The new fallback cleanup is not covered by the added spec; that spec only checks XDG_STATE_HOME. Add a #run example that makes the RSpec subprocess fail and verifies this path is still removed, so the required ensure behaviour cannot regress unnoticed.

        FileUtils.rm_rf HOMEBREW_LIBRARY_PATH/"test/.local"

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Balanced

[Copilot]

🟢 Approval recommended

The cleanup is correctly scoped after worker completion and the new behaviour has focused regression coverage.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0 new
• Review effort level: Balanced

[Copilot]

🟡 Changes recommended

The broad .local ignore masks future state leaks that the redirect is intended to prevent.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Review details

• Files reviewed: 2/3 changed files
• Comments generated: 0 new
• Review effort level: Balanced

[Copilot]

🟢 Approval recommended

The functional change is focused and covered, with only a non-blocking test-convention adjustment remaining.

Review details

• Files reviewed: 2/3 changed files
• Comments generated: 1
• Review effort level: Balanced

[MikeMcQuaid]

Good idea, thanks again!